1. Field of the Invention
The present invention relates to a non-volatile semiconductor memory device such for example as EPROMs and flash EEPPROMs, etc,
2. Description of the Prior Art
TypicaI non-volatile semiconductor memory devices conventionally include EPICOHs, flash EEPROMs, mask ROMs, and the like. For inspecting such non-volatile semiconductor memory devices or monitoring characteristics of memory cells, use is chiefly made in prior practice of a technique to read/write data from/in a memory device from the outside of the memory device, i,e, characteristics of a memory cell can only be viewed from the outside indirectly.
There is known for example as the technique to inspect memory devices a method wherein "0" or "1" is written in memory cells which is read out in turn and compared with each other in a bit unit to inspect whether or not an accurate write/read operation is achieved.
In the cases where the yield of articles is desired to be increased in a wafer process and failure product analyses are performed in a shipping/inspection process or after shipping, there frequently occur an inexpedient situation where it is insufficient only with the foregoing indirect technique and hence a need is produced of directly observing electric characteristics of memory cells, say, a drain voltage-drain current characteristic.
In prior art non-volatile semiconductor memory devices, however, such observation of tile electric characteristics of memory cells was obliged to rely upon laborious techniques such as probing using a needle. Even such probing was also impossible technically to be realized because of the recent progress of fine patterning of the wafer process, and made it impossible to directly observe the, electric characteristics of memory cells and lowered the yield of articles and the accuracy of analyses of failure articles.
To solve the problems with the prior art, it is an object of the present invention to provide a non-volatile semiconductor device wherein electric characteristic of memory cells allow a direct measurement thereof, and the yield of articles and the accuracy of failure article analyses can be improved.